Optimizing Crops for Biocontrol of Pests and Disease Johan A. Stenberg, Martin Heil, Inger Åhman, Christer Björkman  Trends in Plant Science  Volume 20, Issue 11, Pages 698-712 (November 2015) DOI: 10.1016/j.tplants.2015.08.007 Copyright © 2015 The Authors Terms and Conditions

Figure 1 The Push–Pull System. The push–pull system mainly consists of intercropping the crop of interest (here maize) with a plant species that emits volatile organic compounds (VOCs) that repel the major pest. Planting an attractive (pull) plant around the field further enhances directional movements of the pest insect out of the field. Ideally, the pull plant does not allow the pest to reproduce, and both push and pull plants also serve other functions, for example, as ornamental plants, vegetables, spices, or as food for livestock (see [39,40] for details). Trends in Plant Science 2015 20, 698-712DOI: (10.1016/j.tplants.2015.08.007) Copyright © 2015 The Authors Terms and Conditions

Figure 2 Direct Resistance-Related Effects of Volatile Organic Compounds (VOCs). Multiple plant VOCs that are released from damaged tissue or from intact tissue in response to damage in other tissue, such as linalool, can repel herbivores [35,126], and compounds such as nonanal, decanal, and limonene have antimicrobial properties [62]. Owing to their direct nature, these effects should be less context-dependent than the more indirect mechanisms. Trends in Plant Science 2015 20, 698-712DOI: (10.1016/j.tplants.2015.08.007) Copyright © 2015 The Authors Terms and Conditions

Figure 3 Key Figure: The Attract and Reward Concept (A) The emission of HI-VOCs from non-infested plants, or luring parasitoids and predators by artificially dispensing attractive compounds such as MeSA, represent erroneous information that negatively affects the fitness of the attracted biocontrol organisms. Therefore, the additional provision of a reward such as floral or extrafloral nectar, EFN in panel (B), can enhance the survival and efficiency of parasitoids and predators, and thus allow the establishment of more stable populations of these biocontrol organisms ([25,103] for details). Abbreviations: EFN, extrafloral nectar; HI-VOC, herbivore-induced VOC; MeSA, methyl salicylate; VOC, volatile organic compound. Trends in Plant Science 2015 20, 698-712DOI: (10.1016/j.tplants.2015.08.007) Copyright © 2015 The Authors Terms and Conditions